ABSTRACT Reflecting on the world's trend on saving crude oil consumption and to create an economical fuel efficient vehicle for the increasing world population, a new THS-II HV powertrain has been developed for the compact vehicle class. The application of a THS type powertrain for the compact vehicle class was a first for the world and to achieve it, brand new hardware, and software needed to be developed. For the Internal Combustion Engine (ICE), state of the art technologies such as the use of the Atkinson cycle with Variable Valve Timing (VVT), cooled exhaust gas recirculation (EGR), an electric water pump, a compact exhaust manifold, a Low Friction chain, beltless system and exhaust heat recovery system were applied. For the electric motor, copper wire with a rectangular cross section and divided stator cores combined with a newly developed production process were applied for higher volumetric density. For the transaxle; parts location, bearing specifications, and the cooling systems were redesigned to be more compact. Finally, the transaxle and motor were downsized by 21mm in length and weight was reduced by 10.7 kg. This resulted in yielding the best motor power within the space restriction. The HV battery was also relocated under the rear seat to maximize space for competitiveness with non HEV vehicles in the compact class. Toyota's new compact HV “Prius-C” is equipped with this HV powertrain. Prius-C is positioned as the smallest vehicle in the Prius family. Its mission is to offer affordable price, great fuel economy, and convenience for our customers. To improve real world fuel economy, several new control systems were developed. For example, catalyst warm-up time after engine cold start was reduced by 24%, and enginerunning time for SOC recovery in congested traffic was reduced by 67% compared with the current Prius. HV SYSTEM OUTLOOK AND CONFIGURATIONS Same as previous THS-IIs, the Prius-C's HV system consists of an ICE, a transaxle with two electric motors, an inverter- converter and a high voltage battery. However, for downsizing and better fuel economy, several hardware and software improvements have been made from the current Prius. The basic system configuration is as follows: PRIUS-C'S FEATURES COMPARED TO THE CURRENT PRIUS Body mass was reduced from 1397kg to 1132kg, and system net power was reduced from 134hp to 99hp so the power to weight ratio has changed from 10.4 to 11.4. Acceleration time from 0 to 60 mph is increased from 10.2 sec. to 11.4 sec, a difference of 1.2 sec. Although the 0 to 60 mph time has increased, the subjective power feeling is minimal thanks to only a small change in the power to weight ratio and improved software tuning. As a result, Prius-C achieved acceleration performance of the top class in the vehicles in same class. For fuel economy, the combine FE label is 50 mpg which is the same as the current Prius. However, since the Prius-C is a compact model, and considering the character and use of the vehicle, cold FE was optimized as a priority more than the hot FE. As a result, the hot FE was decreased from 48 to 46mpg while the cold FE was increased from 51 to 53 mpg. This change greatly helps real world fuel economy, especially from drivers with frequent short trips. Development of the New THS-II Powertrain for Compact Vehicles2012-01-1017 Published 04/16/2012 Takashi Uehara, Yasuhiro Takahashi, Ryoji Oki, Takahiko Hirasawa, Yusuke Kamijyo, Ikuo Ando, Ryuta Teraya and Makoto Nakamura Toyota Motor Corporation Copyright © 2012 SAE International doi:10.4271/2012-01-1017Downloaded from SAE International by American Univ of Beirut, Saturday, July 28, 2018Table 1. HV system configurations of Prius-C Figure 1. Battery and fuel tank installation for maximum luggage space Figure 2. Dimensions of luggage space Cabin and luggage space of the Prius-C was not compromised and is competitive when compared with non HEVs in the compact class (see table 2). This is mainly dueto the installa